Spray- and flame-wall interactions were investigated in a combustion chamber with diesel engine conditions. Several techniques were used to perform time and spatially resolved measurements of the liquid fuel phase, the premixed and diffusion-controlled combustion close to a wall.
Different wall and gas temperature variations were investigated. It was found that low temperature variations of 25K have a significant impact on the combustion process:
The lower the gas temperatures, the more liquid fuel and larger vortex structures arise. Also, the ignition delay is elongated. Consequently, the premixing period is longer, which can lead to the complete disappearance of sooty combustion.
The colder the wall, larger cooling of the spray and larger vortex structures of liquid fuel on the wall develop. The ignition delays again are noticeable longer at the colder wall. Therefore, the premixing period is longer and there is also much less sooty combustion when the wall temperature is lower.
Further, a reference fuel following the European normative EN 590 (CEC) and a rapeseed fuel (RME) were compared. The ignition delay of CEC is shorter than that of RME. This is remarkable, since measurements without wall interaction showed the opposite. It is important for the spray-wall- interaction whether the fuel is liquid or vaporized when the interaction takes place, because of an intensified heat exchange in the case of liquid wall interaction.